I think it means Newt paid tax on his earned income, compared to Romney's income which was mainly investment income which was taxed at the current capital gains rates. This corresponds to Romney's statement of having little earned income. Which got me to wondering what he thought a little was. I saw a story on fox saying what they had researched so far showed $360,000 in earned income for Mitt last year.
This kind of 'hide the pumpkin while I run with it', type of attitude is not conducive to voter support, IMHO.